Ok, I admit I'm degrading. More and more I've found myself wondering about projects and stuff related to shortwaves, which I was not at all interrested in the past. It might sync with the gray hair? :)
The 14 MHz low pass filter needs bit tweaking as the insertion loss starts to increase bit too early, having already about 2.5 dB loss at the 14 MHz band. It still works for my purposes as I plan to make 80m and 40m RTL-SDR receivers.
The 28 MHz low pass filter performs as should, the insertion loss starts to increase about at 30 MHz. The attenuation curve could be bit deeper but this is a good start to put in the front of the RTL-SDR's
Anyway, the RTL-SDR technology and development which I've been following closely has made me want to make few direct-sampling RTL-SDR based receivers for the community use through the WebSDR's I run.
I bounced to a universal low pass filter kit at W8DIZ Kits and Parts online shop. I purchased few kits, one for lower HF bands and another to cover up to 28MHz. The kits were $8 each, shipping was $14,40 which is hilarious in the relation to the price of the actual goods :)
The kits arrived in the mail pretty fast, including small bags for each filter ordered.
Constructing the kits was easy and I just was able to measure the filters with my DG8SAQ VNWA.
Insertion loss is the blue curve, return loss (matching) is the red curve. In general the filter responses are as expected. Insertion los at the passband section is only fractions of a decibel so they will work great for a RX project.
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| 14 MHz low pass filter insertion and return loss measurements |
The 14 MHz low pass filter needs bit tweaking as the insertion loss starts to increase bit too early, having already about 2.5 dB loss at the 14 MHz band. It still works for my purposes as I plan to make 80m and 40m RTL-SDR receivers.
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| 28 MHz low pass filter insertion and return loss measurements |
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